1. Field of the Invention
The present invention relates to a switching device, and more particularly to a switching device for a transfer switch and that can automatically switch to an auxiliary power source when a main power source being cut off.
2. Description of Related Art
A building, such as a manufacturing plant or hospital is always connected to a main power source and an auxiliary power source that provides electrical power to the building when the main power source is cut off. Therefore, a transfer switch is always electrically connected between the main and auxiliary power sources to switch the electrical connection of the building to the power sources.
With reference to FIG. 10, a conventional transfer switch comprises a base (80) and a switching device (90). The base (80) has two contacting tags (81,82) respectively connected electrically to a main power source and an auxiliary power source.
The switching device (90) comprises two solenoids (83), a switching rod (91), an extension arm (92), a pivot (94) and two resilient members (93). The solenoids (83) are mounted on the base (80) and face to each other. Each solenoid (83) has a driving shaft (84) driven by electromagnetic power generated by the solenoid (83) and extends toward the driving shaft (84) of the other solenoid (83). A connecting linkage (85) is mounted between the driving shafts (84) of the solenoids (83) and has an elongated hole (851) defined through the connecting linkage (85).
The switching rod (91) is pivotally connected to the base (80) by the pivot (94) and has a first end, a second end and a middle. The first end is connected to the pivot (94) for pivotally connection with the base (80). The second end is provided with a connector (95) selectively abutting with one of the connecting tags (81,82) on the base (80) and electrically connected to a power system of a building. A sliding rod (911) is mounted on the middle of the switching rod (91) and is slidably held in the elongated hole (851) in the connecting linkage (85). The extension arm (92) is laterally formed and protrudes from the first end of the switching rod (91) and has two ends. The resilient members (93) may be springs and are connected respectively to the ends of the extension arm (92) and the base (80).
With the contact between the connector (95) and the connecting tag (81) connected to the main power source, the electrical power provided by the main power source can be led to the building. When the main power source is cut off, one of the solenoids (83) corresponding to the auxiliary power source is actuated and retracts the driving shaft (84) of the solenoid (83). Consequently, the driving shaft (43) of the other solenoid (83) connected to the main power source will be extended out to make the connecting linkage (85) moving toward the solenoid (83) corresponding to the auxiliary power source. With the movement of the connecting linkage (85), the switching rod (91) is pivoted relative to the base (80) with the resilient force provided by the resilient members (93). Accordingly, the connector (95) on the switching rod (91) is switched to contact with the connecting tag (82) connected to the auxiliary power source. Thus, the building is provided with electrical power by the auxiliary power source.
When the main power source recovers, the switching rod (91) is pivoted in reverse to make the connector (95) contacting with the connecting tag (81) connected to the main power source.
However, the conventional transfer switch comprises two solenoids (83), but the solenoids (83) are at a high cost and take large spaces for arrangement. Therefore, the manufacturing cost for the transfer switch is high.
To overcome the shortcomings, the present invention tends to provide a switching device to mitigate or obviate the aforementioned problems.